Reclamation device for gas-type circuit interrupters



Oct. 12, 1965 A. P. STROM 3,210,952

REGLAMATION DEVICE FOR GAS-TYPE CIRCUIT INTERRUPTERS Original Filed Dec.9, 1958 2 Sheets-Sheet 1 Vapor Pressure of Sulfur Hexafluoride at verylow Temperatures Temperature of CO Ice at l Arm.

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RECLAMATION DEVICE FOR GAS-TYPE CIRCUIT INTERRUPTERS Original Filed Dec.9, 1958 2 Sheets-Sheet 2 v 23.. 53 u a: w E

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46 L 2 Q I 44 v M Q United States Patent 3,210,952 RECLAMATION DEVICEFOR GAS-TYPE CIRCUIT INTERRUPTERS Albert P. Strom, Forest Hills, Pa.,assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Continuation of application Ser. No.779,103, Dec. 9, 1958. This application Dec. 11, 1961, Ser. No. 159,821

5 Claims. (Cl. 62-40) This application is a continuation of my patentapplication filed December 9, 1958, Serial No. 779,103 and nowabandoned.

This invention relates to reclamation devices for gastype circuitinterrupters, and, more particularly, to a liquefaction-type reclamationdevice for collecting and liquefying gas from gas-type circuitinterrupters during .the maintenance thereof.

As well known by those skilled in the art, it is advisable periodicallyto open circuit interrupters, inspect the contact structures thereof andto make necessary adjustments as well as replace worn parts. In the caseof a .gas-type circuit interrupter, when this maintenance operationtakes place and the casing enclosing the arc-extinguishing gas is openedfor such inspection purposes, a decision must be made as to whether theenclosed gas used for arcextinguishing purposes is to be freelydissipated to the atmosphere, and hence lost, resulting in the necessityfor a fresh charge of arc-extinguishing gas during the subsequent returnof the circuit interrupter into operation, or whether thearc-extinguishing gas is to be collected and reclaimed during thisinspecting operation.

The aforesaid decision may hinge on economics, and if thearc-extinguishing gas used in the gas-type circuit interrupter -issufi'iciently expensive, and if the volume and pressure of thearc-extinguishing gas is considerable, it is advisable to provideapparatus for effecting the collection and reclamation of thearc-extinguishing gas, so that it may subsequently be used in the sameor similar circuit interrupters when such circuit interrupters arereturned to active duty on the transmission system.

It is a general object of the present invention to provide an improved,portable, reclamation device suitable for the connection to gas-typecircuit interrupters so that the gas from the circuit interrupter may becollected and stored within the reclamation device.

A more specific object of the present invention is to provide animproved reclamation device suitable for the detachable connection to agas-type circuit interrupter, in which gas from the circuit interruptermay be collected and liquefied by suitable cooling and condensing meansso that the resulting liquefied arc-extinguishing gas may .be collectedin a storage tank associated with the aforesaid reclamation device forsubsequent use in the same or similar gas-type circuit interrupters.

A further object of the invention is to provide an improved reclamationdevice having associated therewith a condensing chamber, within which isdisposed a suitable condensing coil and having means provided foreffecting Patented Oct. 12, 1965 ice proved reclamation device suitablefor collecting and liquefying arc-extinguishing gas from a circuitinterrupter during periodic maintenance inspection periods, in which twocoolant agents are employed in the condensing coil of the reclamationdevice to save expense of operation.

Further objects and advantages will readily become apparent upon readingthe following specification, taken in conjunction with the drawings, inwhich:

FIGURE 1 is a curve of the vapor pressure of sulfur hexafluoride at verylow temperatures; and

FIG. 2 illustrates in vertical cross-section, and partiallydiagrammatic, the reclamation device of the present invention associatedwith a circuit interrupter of the gastype.

As well known by those skilled in the art, particularly in recent years,investigations have resulted in the determination of the extremely highinterrupting performance of certain arc-extinguishing gases. Sulfurhexafluoride (SP is such a gas and is relatively expensive. Theproperties of sulfur hexafluoride for circuit interruption are set outin detail in United States Patent 2,757,261, issued July 31, 1956 toHarry I. Lingal, Thomas E. Browne, In, and Albert P. Strom, and assignedto the assignee of the instant application. The use of sulfurhexafluoride for circuit interruption has been extensive, being employedfor circuit interrupters of the load-break disconnecting switch type,such as illustrated in United States Patent 2,769,063, issued October30, 1956, to Harry J. Lingal, and assigned to the assignee of theinstant application. In addition, sulfur hexafluoride has been used inconnec tion with power interrupters, such as set out in United StatesPatent 2,748,226, issued May 29, 1956, to John B. MacNeill and BenjaminP. Baker, and likewise assigned to the assignee of the instantapplication.

Selenium hexafiuoride (SeF is also a very powerful arc-extinguishing gasand is likewise expensive. It is described and claimed in United StatesPatent 2,733,316, issued January 31, 1956, to Thomas E. Browne, Jr.,Albert P. Strom and Harvey E. Spindle, and assigned to the assignee ofthe instant application.

Although the present invention is suitable for use with a number ofarc-extinguishing gases, for purposes of simplicity and clarification ofthe invention, the invention will be described as particularly appliedto a circuit interrupter employing sulfur hexafluoride (SF gas as thearcextinguishing medium, without any intention of limiting the broaderaspects of the invention to this particular gas.

Sulfur hexafluoride gas has been shown to be an excellent circuitinterrupting medium, as set out in United States Patent 2,757,261, andis already being used for this purpose in many recently developedcommercial circuit interrupters. It is a relatively expensive gas atpresent, the present price being $2.25 per pound of gas, or about 10 pergallon per atmosphere. Since the gas pressure normally used in thecircuit breakers is about 4 or 5 atmospheres, the cost of filling an SPbreaker is about 40 to 50 per gallon, or somewhat more than for an oilcircuit breaker of equal volume. This makes it rather desirable to saveand to reclaim this gas when a breaker is to be opened for servicing.

The sulfur hexafluoride gas could be drawn by a compressor out of thebreaker down to about atmospheric pressure, and subsequently compressedinto a storage cylinder. To remove the gas to a pressure below that ofatmospheric pressure, a vacuum pump would have to be used in series withthe compressor. If the gas is pumped into the storage cylinder at normaltemperature, it will be necessary to compress the gas to about 350-400p.s.i. This consequently requires relatively expensive compressingequipment, as well as the use of a vacuum pump.

It is proposed in the present invention, however, to

provide a method and means whereby the SP gas may be removed from thebreakers and collected in a storage cylinder, which is much moreconvenient and considerably less expensive. The proposed method of thepresent invention is that of freezing out the sulfur hexafiuoride gas bythe use of carbon dioxide ice or with liquid nitrogen, or, in fact,utilizing both coolant agents in sequence.

The vapor pressure curve for sulfur hexafluoride (SP at temperaturesbelow those for liquefaction at atmospheric pressure is illustrated inFIG. 1. This curve shows that at point A, namely substantially at 78 C.,the temperature of Dry Ice, the vapor pressure of SP is about 300millimeters, or approximately 0.4 atmosphere. It is thus possible toreduce the pressure in a sulfur hexafiuoride gas-type breaker to 0.4atmosphere, by simply cooling the gas storage cylinder connected to thebreaker volume with Dry Ice, or solid carbon dioxide.

The cost, at present, of Dry Ice or solid carbon dioxide, is only about4 per pound. The cooling effect may be calculated as follows:

The latent heat of vaporization of CO is about 80 calories per gram at78 C. Hence, a pound of evaporating CO absorbs about 80x454=36,000calories. The latent heat of vaporization of SP is about 35 calories pergram. The specific heat (Cp) is about 0.2 calorie/ gram/degree. Hence,to cool and to condense one pound of SE, from 20 to 78 C., requiresapproximately (0.2 98+35) 454=24,500 calories.

Thus, neglecting heat losses, one pound of SP can be cooled to -78 C.,and condensed with about at a cost of 0.68 4=2.75 cents.

It is of interest to note that in a particular 3-pole, 115 kv., SPbreaker, a total of about 24 pounds of SP gas will be used atatmospheric pressure. If this is removed and saved down to 0.4atmosphere by means of Dry Ice, 90% of the SP gas, or 21.6 pounds can berecovered. The cost, assuming 50% efficiency, would be There would stillbe about 2.4 pounds of SP gas left in the breaker worth approximately$4.80, which could not be salvaged.

However, if liquid nitrogen (N is used instead of Dry Ice, a temperatureof l95 C. can be reached. At

=0.68 pounds of Dry Ice this temperature, the pressure of SE, will be inthe order =l.7 pounds of liquid nitrogen The density of liquid nitrogenis 0.808, or weight per liter 808 grams 1.78 pounds.

It thus appears that about 1 liter of liquid nitrogen is required tocondense 1 pound of SP The cost of liquid nitrogen per liter is about15. Hence, the total cost to condense the 24 pounds of gas in thebreaker discussed above would be 15 24=$3.60, neglecting heat losses or$7.20, assuming 50% efiiciency. Thus, while the cost per pound ofcondensed SP is less with Dry Ice, when the cost of the SP which cannotbe salvaged is included,

4 it appears as if the net cost for either Dry Ice or liquid nitrogenmight be about equal.

The foregoing calculations indicate that with suitable equipmentinvolving proper heat exchangers, it is quite practical to use freezeout methods for recovering or reclaiming SP gas from circuit breakers,and, more importantly, in many cases it saves the investment inexpensive compressor equipment.

With the foregoing principles in mind, there will now be described animproved circuit interrupter having associated therewith a condensablecooling means generally designated by the reference numeral 1 in FIG. 2of the drawings. With reference to FIG. 2, it will be noted that thecondensable cooling means 1, or portable reclamation device, includes acondensing chamber 2 having an inlet 3 leading from a detachableconnection 4 to a gastype circuit interrupter, generally designated bythe reference numeral 5.

Generally, the circuit interrupter 5 contains a relatively expensivearc-extinguishing gas 6, which may be SP SCFG, CO2, CF3B1', CZFG, SOFZ,CCIFQ, C2ClF3, S02, C 1 OCI F C1031: or CF SF Disposed interiorly withina casing 7 of the circuit interrupter 5 is a relatively stationarycontact 8, which cooperates with a movable contact 9, the latter beingassociated with a piston structure 10 and withdrawn upwardly, during theopening operation, by a conductor operating rod 11. A terminal 12 isassociated with the upper end of the conducting operating rod 11. Anadditional terminal 13 is connected to the base 14 of the relativelystationary contact 8. An apertured metallic piston plate 15 isthreadedly secured to the lower extremity of the conducting operatingrod 11. The outer periphery of the piston plate 15 is preferablythreadedly secured to the upper end of a piston sleeve 16, the lattersupporting a movable orifice structure 17 therewith. The details ofconstruction of the piston structure 10 are more fully set out andclaimed in United States Patent 2,757,261 referred to hereinbefore.

For the purpose of understanding the present invention, it is onlynecessary to know that the operating rod 11 moves upwardly during theopening operation through a gas-tight seal 18 causing the separationbetween the lower end of the movable contact 9 and the stationarycontact 8. This, of course, establishes an arc therebetween interiorlyof the sealed casing 7. Since the apertured piston plate 15 is securedto, and movable with, the lower end of operating rod 11, it will beapparent that the orifice structure 17 is carried upwardly during theopening operation.

The arc-extinguishing condensable gas 6, disposed within the region 19in back of the piston structure 10, will be forced through the apertures20 in apertured piston plate 15 and through the orifice 21 associatedwith the orifice structure 17, causing thereby a longitudinal compressedflow of gas 6 adjacent the established arc between contacts 8, 9effecting the rapid extinction thereof. The circuit between theterminals 12, 13 will then be broken.

Communicatnig with the upper end of the casing 7 of the circuitinterrupter 5 is a gas conduit 22. A bore 23 through a guide sleeve 24insures communication between the conduit 22 and the interior 19 of thecasing 7.

Preferably, a cutoff valve 25 is provided, so that when the casing 7 ischarged with a suitable condensable arcextinguishing gas 6, the valve 25may be closed and the circuit interrupter 5 will then be adapted forindependent operation.

As stated hereinbefore, however, it periodically becomes necessary tomaintain, or service the gas-type circuit interrupter 5, and when thisis done, the casing 7 will be opened for inspection purposes. To preventthe loss of the relatively expensive arc-extinguishing gas 6, thecondensable cooling means 1 is provided. As shown in FIG. 2, a coupling26 detachably interconnects the exhaust tube 4 with the gas conduit 22.In addition, a second coupling 28 detachably interconnects the exhausttube 4 with an inlet tube or inlet pipe means 29 leading to the inlet 3of reclaiming device 1. The inlet tube 29 is of T-shaped configurationhaving a branch conduit 30 leading, through a cutoif valve 31, to asource of vacuum, not shown. The branch conduit 30 and the cutolf valve31 constitute a valve-controlled vacuum-pipe means, generally designatedby the reference numeral 60.

The upper end of the condensing chamber 2 is controlled by a valve 32.The valve 32 is provided for closing the passage from the gas chamber orcasing 7 of circuit interrupter 5 to the condensing chamber 2. Acondensing coil 33 extends from the bottom of condensing chamber 2 intothe interior thereof, and for ease of manufacture and assembly, thecondensing coil 33 is shown as attached to a plate 34, which is bolted,by bolts 35 to chamber 2. Preferably, a gasket 36 is employed to providea gas tight connection. Thus, the plate 34 forms the bottom of thecondensing chamber 2.

Connections for the condensing coil 33 are brought out at 37, 38. Acontainer cup 39 is provided to hold the-cooling fluid. If carbondioxide ice is used, a low freezing point liquid, such as acetone oralcohol, can be used with 'it as a heat transfer liquid. A screen 40prevents any solid particles from entering the condensing coil33. Thecoolant liquid 41 then passes through the pump, 42, into tube 37,through condensing coil 33, through tube 38 and tube 43 back to the cup39. If the pump means 42 is not available, the coolant liquid may becirculated through the coils 33 by opening valve 44, collecting theliquid in storage tank 45 and pouring it back manually into thereservoir chamber, or container cup 39.

With a solid carbon dioxide and acetone system, it should be possible tocool the coils 33 to about -78 C. This will condense the sulfurhexafluoride (SP to about 0.3 or 0.4 atmosphere. The pressure withincondensing chamber 2 will then fall to less than 1 atmosphere, andconsequently, the gas from the casing 7 of circuit inter-. rupter 5 willbe drawn into the condensing chamber 2 and liquefied. One difficulty,however, is that in the case of SF gas, it has a melting point of 56 C.,which is reached at slightly above atmospheric pressure, and as thepressure in condensing chamber 2 falls to below atmospheric pressure,the SE; gas may condense as a solid on the cooling coil 33. This mighttend to heat insulate the cooling coils 33, greatly reducing the rate ofcondensation of SF gas.

However, to de-ice the coils 33, it is necessary only to raise thetemperature to '56 C. For such a de-icing operation, a heating element61 comprising a heater coil 46 is provided. This coil 46 may be woundwith preferablyglass or polytetrafluoroethylene-insulated resistancewire, directly onto the cooling coil tubes 33. During the de-icingoperation, the cooling fluid 41 may be drawn oif through the tube 47 tothe collecting tank 45 (although this is not always necessary) byopening valve 44. Current may then be applied to the heating element 61by means of the plug 48 connected to a suitable 110-volt, A.C. supply,for example. Valve 32 should be closed since the pressure will rise to 5or p.s.i.g. in condensing chamber 2. Valves 49 and 50 should now beopened to transfer all of the condensed liquid SP collected incondensing chamber 2 into storage chamber or tank 51. As soon as thepressure within condensing chamber 2 has risen to about 10 p.s.i.g. ongauge 52, indicating all ice has melted, condensation may proceed again,heater current through heater coil 46 can be stopped, cooling liquid 41may again be recirculated, valves 49, 50 closed and inlet valve 32opened.

To remove the last 0.4 atmosphere of SF gas, a small quantity of liquidnitrogen is used in container cup 39, replacing the carbon dioxide, DryIce solution. The remaining gas will then condense on the cooling coils33 in the form of ice or snow, which may be melted off at intervals, aspreviously described by the de-icer coil 46,

6 the liquid then being transferred to storage bottle or tank 51.

In the process of evacuating the gas in this manner, it is also possibleto clean it of any are products. Most of these can be removed by meansof an activated alumina filter 53 in the inlet line 29. CR, gas,however, may pass through the filter 53 into the condensing chamber 2.However, this CF gas may be drawn off by closing valves 25, 49 and 50,cooling the condensing chamber 2 to the lowest possible value, andapplying a vacuum for a few moments to branch outlet 30 opening valve31. The GE; gas will come off from the condensing chamber 2 since it hasa much higher vapor pressure than SF gas.

It will be observed that the casing 54 has an upper open end, andcontains a heat insulation material 55, such as glass wool. The casing54 is preferably portable as indicated by the wheels 56 and trailerhitch 57. Thus, the reclamation device may be easily transported todifferent circuit interrupters, and following the exhausting of thearc-extinguishing gas from one circuit interrupter 5, the couplings 26,28 may be removed, and the reclamation device 1 may be wheeled toanother circuit interrupter 5 during the latters maintenance period.Thus, the reclamation device 1 may be employed to service a number ofisolated circuit interrupters 5.

From the foregoing description, it will be apparent that there isprovided an improved reclamation device associated with one or morecircuit interrupters adaptable for freezing out or liquefyingcondensable arc-extinguishing gas employed in such circuit interrupters.By such reclaiming operations, the expense involved in supplying freshgas is avoided, and the expense entailed in supplying carbon dioxide DryIce or liquid nitrogen is insignificant compared to the saving inexpense resulting from reclaiming the arc-extinguishing gas.

Although the invention has been specifically described, and isparticularly advantageous in conection with sulfur hexafluoride gas (SPit is to be clearly understood that such gas was used only for purposesof illustration and that, in fact, the reclamation device lot thepresent invention may be used with circuit interrupters employing othergases, such as enumerated above with advantage. As mentioned, theportability of the reclamation device 1 renders it suitable forservicing a large number of circuit interrupters 5 of the gas-typeduring periodic inspection periods.

The following are possible gases that may be used with their boilingpoints and possible coolants for their condensation:

Arc-Extinguish- Liqiligd air or liquid N2 or solid 00:.

D0. D0. Liquid air, or liquid N and solid 00;. Llq%d air or liquid N; orsolid 00;.

Do. Liquid air or liquid nitrogen. Liquid air or liquid N or solid CO2.Liquid air, or solid CO2 and liquid N2- Liquid air, nitrogen or solid002.

Although there has been shown and described only a single reclamationdevice, it is to be clearly understood that the same was merely for thepurpose of illustration, and that changes and modifications may readilybe made therein by those skilled in the art without departing from thespirit and scope of the invention.

I claim as my invention:

1. A portable liquefaction-type of reclamation device for detachableconnection with gas-type circuit interrupters for reclaiming thearc-extinguishing gas therein during servicing operations including aportable truck carrying a casing having heat insulating materialdisposed therewithin, a condensing chamber disposed adjacent the upperend of the casing at least partially embedded within said heatinsulating material and having a condensing coil extending therein, aheating element associated with said condenser coil, means forconnecting the heating element to a source of electrical power forperiodically heating said coil for de-icing purposes, a container cupfor containing a coolant fluid, conduit means for interconnecting saidcontainer cup with the condensing coil, a storage tank for collectingliquefied arc-extinguishing gas disposed adjacent the lower end of saidtruck embedded within said heat insulating material, and additionalconduit means interconnecting said storage tank with said condensingchamber, whereby the arc-extinguishing gas from the circuit interruptermay be liquefied and collected within said storage tank.

2. A portable liquefaction-type of reclamation device for detachableconnection with gas-type circuit interrupters for reclaiming thearc-extinguishing gas therein during servicing operations including aportable truck carrying a casing having heat insulating materialdisposed therewithin, a condensing chamber disposed adjacent the upperend of the casing at least partially embedded within said heatinsulating material and having a condensing coil extending therein, aheating element associated with said condenser coil, said heatingelement comprising a. heating coil encircling the condenser coil for anappreciable length, means for connecting the heating element to a sourceof electrical power for periodically heating said coil for deicingpurposes, a container cup for containing a coolant fluid, conduit meansfor interconnecting said container cup with the condensing coil, astorage tank for collecting liquefied arc-extinguishing gas disposedadjacent the lower end of said truck embedded Within said heatinsulating material, and additional conduit means interconnecting saidstorage tank with said condensing chamber, whereby the arc-extinguishinggas from the circuit interrupter may be liquefied and collected withinsaid storage tank.

3. A portable liquefaction-type of reclamation device for detachableconnection with gas-type circuit interrupters for reclaiming thearc-extinguishing gas therein during servicing operations including aportable truck carrying a casing having heat insulating materialdisposed therewithin, a condensing chamber disposed adjacent the upperend of the casing at least partially embedded within said heatinsulating material and having a condensing coil extending therein, aheating element associated with said condenser coil, means forconnecting the heating element to a source of electrical power forperiodically heating said coil for de-icing purposes, a container cupfor containing a coolant fluid, conduit means for interconnecting saidcontainer cup with the condensing coil, pump means for forcing coolantfluid through said conduit means and through the condensing coil, astorage tank for collecting liquefied arc-extinguishing gas disposedadjacent the lower end of said truck embedded within said heatinsulating material, and additional conduit means interconnecting saidstorage tank with said condensing chamber, whereby the arc-extinguishinggas from the circuit interrupter may be liquefied and collected withinsaid storage tank.

4. A portable liquefaction-type of reclamation device for detachableconnection with gas-type circuit interrupters for reclaiming thearc-extinguishing gas therein during servicing operations including aportable truck carrying a casing having heat insulating materialdisposed therewithin, a condensing chamber disposed adjacent the upperend of the casing at least partially embedded within said heatinsulating material and having a condensing coil extending therein,inlet pipe means associated with the upper end of the condensingchamber, valve-controlled vacuum-pipe means connected with the inletpipe means for the extraction of relatively high-vapor-pressurecontaminating gases, a coolant-liquid container cup, conduit meansinterconnecting the container cup with the condensing coil, pump meansfor forcing coolant-liquid through said conduit means and through thecondensing coil, a storage tank for collecting liquefiedarc-extinguishing gas disposed adjacent the lower end of said truckembedded within said heat insulating material, and additional conduitmeans interconnecting said storage tank with said condensing chamber,whereby the arc-extinguishing gas from the circuit interrupter may beliquefied and collected within said storage tank.

5. A portable liquefaction-type of reclamation device for detachableconnection with. gals-type circuit interrupters for reclaiming thearc-extinguishing gas therein during servicing operations including aportable truck carrying a casing open at the upper end thereof andhaving heat insulating material disposed therewithin, a condensingchamber disposed adjacent the upper end of the casing at least partiallyembedded within said heat insulating material and having a condensingcoil extending therein, said condensing chamber being removable from thetruck through the upper open end of said casing, a heating elementassociated with said condenser coil, means for connecting the heatingelement to a source of electrical power for periodically heating saidcoil for de-icing purposes, a container cup for containing a coolantfluid, conduit means for interconnecting said container cup with thecondensing coil, a storage tank for collecting liquefiedarc-extinguishing gas disposed adjacent the lower end of said truckembedded within said heat insulating material, and additional conduitmeans interconnecting said storage tank with said condensing chamber,whereby the arcextinguishing gas from the circuit interrupter may beliquefied and collected within said storage tank.

References Cited by the Examiner UNITED STATES PATENTS 2,328,647 9/43Jackson 629 2,511,419 6/50 Smith 62-275 2,571,014 10/51 Colburn et a162-12 2,738,658 3/56 Bronson 6210 2,895,303 7/59 Streeter.

2,955,182 10/60 Caswell et a1 ZOO-448.2 2,955,807 10/60 Riley et al.62275 FOREIGN PATENTS 287,486 6/29 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

ROBERT A. OLEARY, Examiner.

1. A PORTABLE LIQUEFACTION-TYPE OF RECLAMATION DEVICE FOR DETACHABLECONNECTION WITH GAS-TYPE CIRCUIT INTERRUPTERS FOR RECLAMING THEARC-EXTINGUISHING GAS THEREIN DURING SERVICING OPERATIONS INCLUDING APORTABLE TRUCK CARRYING A CASING HAVING HEAT INSULATING MATERIALDISPOSED THEREWITHIN, A CONDENSING CHAMBER DISPOSED ADJACENT THE UPPEREND OF THE CASING AT LEAST PARTIALLY EMBEDDED WITHIN SAID HEATINSULATING MATERIAL AND HAVING A CONDENSING OIL EXTENDING THEREIN, AHEATING ELEMENT ASSOCIATED WITH SAID CONDENSER COIL, MEANS FORCONNECTING THE HEATING ELEMENT TO A SOURCE OF ELECTRICAL POWER FORPERIODICALLY HEATING SAID COIL FOR DE-ICING PURPOSES, A CONTAINER CUPFOR CONTAINING A COOLANT FLUID, CONDUIT MEANS FOR INTERCONNECTING SAIDCONTAINER CUP WITH THE CONDENSING COIL, A STORAGE TANK FOR COLLECTINGLIQUEFIED ARC-EXTINGUISHING GAS DISPOSED ADJACENT THE LOWER END OF SAIDTRUCK EMBEDDED WITHIN SAID HEAT INSULATING MATERIAL, AND ADDITIONALCONDUIT MEANS INTERCONNECTING SAID STORAE TANK WITH SAID CONDENSINGCHAMBER, WHEREBY THE ARC-EXTINGUISHING GAS FROM THE CIRCUIT INTERRUPTERMAY BE LIQUEFIED AND COLLECTED WITHIN SAID STORAGE TANK.